. "Upon phosphorylation of the R-SMAD (SMAD2/3), the conformation of the C-terminal (MH2) domain of the R-SMAD changes, lowering its affinity for the type I receptor and SARA. As a result, the phosphorylated R-SMAD dissociates from the activated receptor complex (TGFBR)."^^ . . . . . . . . .